The Defense Ministry has doubled the number of fighter jets it scrambles when responding to airspace checks by foreign planes, government sources said Saturday.

The Air Self-Defense Force began scrambling four jets for each potential airspace violation last year, they said. The ASDF had previously been sending up only two jets per scramble since it began the practice in 1958.

As China ramps up its military activities around the Senkaku Islands in the East China Sea, scramble intercepts by both sides have been surging in areas nearby where their air defense identification zones overlap. The Japan-administered Senkakus, which lie just off Taiwan, are also claimed by China and Taiwan.

Tokyo and Beijing have yet to set up a communication mechanism that can be used by their militaries to avoid accidental aerial or maritime clashes.

The number of scrambles launched between last April and this January has already eclipsed the annual record of 944 set in fiscal 1984, when the Cold War was in full swing and airplanes from the former Soviet Union were active.

According to the sources, an increasing number of Chinese aircraft have been flying past 27 degrees north latitude, which Japan considers a defensive border line. Japan’s goal is to keep Chinese planes out of the area between 25 and 26 degrees latitude, which encompasses the Senkakus.

Of the four F-15s scrambled each time, two in the rear will be on alert to deal with any additional aircraft that join the incursion.

The ASDF has also extended the duration of its combat air patrols and begun sending up more E-2C early warning aircraft and airborne early warning and control system (AWACS) planes for scrambles.

In January last year, the Defense Ministry doubled the number of F-15s stationed at its base in Naha, Okinawa Prefecture, to about 40, but more frequent scrambles and an increase in fighter jets deployed for each mission created a shortage of jets on standby.

To operate more flexibly, the air defense command in Tokyo has started controlling fighter jets across different regions, reviewing such rules as the minimum number of aircraft needed for standby at each composite air division.